The following images (click on them for larger versions) show how the observation head and covers are attached.
The compenents here are the observation head body, photomask reticle on a linear dovetail, 1x relay lens, the observation turret which contains an open position for normal use, a closed position for microphotography, a 2x magnifing lens for low power focusing, and a Bertrand lens for Koehler illumination, phase ring and Hoffman Modulation Contrast mask alignment. It also then goes to the binocular splitting prism assembly and eyepiece (occular) observation tubes.
The other very common component to be frozen due to age is the Bertrand lens focusing mechanism. This is another one that is difficult to fix without contaminating the Bertrand lens itself.
Once again, the linear dovetail tends to be stiff or frozen. Unfortunately, this one cannot be reached for servicing without some disassembly, either by removal of the entire observation head body or the relay lens assembly.
Taking the observation head body off of the main body is the place where a long T-handle hex wrench is very useful.
Next, I replaced the sample stage.
for navigation!